Screw pump



March 25, 1952 c. o. T. MoNTELlUs SCREW PUMP Filed Sept. 25, 1948INVENTOR CARL OSCAR TORSTE/V MONTEL/US *..f my www w w Q kfw N v/ v BY/M cY Y TTORN YS Patented Mar. 25, 1952 UNITED STATES ?ATENT OFFICEApplication September 25, 1948, Serial No. 51,135 In Sweden May 10, 1948(Cl. S-128) 5 Claims.

The present invention relates to screw-pumps and motors comprising twoor more intermeshing screw-rotors enclosed in a closely fitting sleevehaving intersecting bores. In order to obtain high pump pressure it isimportant to maintain a tight t between the threads of the screws asWell as between the screws and the bores in the sleeve, the screwsrotating in the bores in the same manner as shafts in bearings.

The necessity of using long screws and bores makes it diiiicult toobtain an exactly uniform bearing for the screws in 'the bores of thesleeve, as these cannotbe bored or turned to an exactly uniform diameterthroughout, without special precautions. But even if the bores shouldhave an exact sha'pe, they might be slightly deformed through themounting of the sleeve in its casing, or by the stresses from the pipesattached to the casing.

In order to avoid these disadvantages the present invention suggeststhat the sleeve is made in two or more parts independent of each other,which are freely adjustable in relation to one another but act as asingle unit by the working pressure of the pump. The diiferent parts areallowed to adjust th-emselves on the screw-rotors, whereby thedisadvantages caused by using one long, single sleeve are eliminated.

Preferably the part of the sleeve adjacent to the low-pressure side ofthe pump is rigidly connected to or integral with the pump casing, theother part or parts of the sleeve at the highpressure side of the pumpadjusting themselves to the screws. A clearance between said part orparts and the pump casing is desirable in order to allow a properalignment. When the pumpv is started, these movable parts of the sleeveare pressed against the xed part of the sleeve by the liquid pressureacting on the end surfaces.

In order better to hold and locate the parts of the sleeve by the pumppressure, the engaging end surfaces should be shaped to contact eachother near their largest diameters only.

In order to obtain the greatest possible thrust force between themovable and iixed parts of the sleeve, and between the different movableparts if a plurality of such parts are used, not only the engagingsurfaces should be located near the periphery of the end surfaces asmentioned above but also the counter-pressure on the main part of theend surfaces of the sleeve facing each other should be eliminated 'by adrainage passage and a suitable seal.

The general objects of the present invention relate to the attainment ofthe advantages just described. vThese and other objects relatingparticularly todetails oi construction and operation will `becomeapparent from the following descrip* tion read in conjunction with theaccompanying drawing, in which:

Fig. 1 shows a longitudinal section of a pump operating with threescrews, while Fig. 2 is a cross section of the same.

Figs. 3 and 4 illustrate corresponding sections of a double-screw pump.

In both embodiments the screws are provided with balancing pistonsoperating in self-adjusting sleeves.

In the embodiment illustrated by Figs. 1 and 2 the pump casing is ateach end provided with covers 2 and 3 attached to the pump casing byscrews 4. In a central and preferably cylindrical bore in the casing Iis inserted a sleeve consisting of two parts 5 and 6. The part 5 isaccurately fitted to the casing and kept in :place by a locking bolt 1,while the part G is mounted with clearance. Each of the parts 5 and S isprovided with three parallel, cylindrical and intersecting bores. Ascrew-rotor is mounted in each of these bores, the central rotor 8having left-hand threads and the side rotors 9 having right-handthreads.

The central rotor 8 is provided with a driving shaft Il) projecting withclearance through the cover` 2. Liquid entering through an inlet II to achamber I2 is trapped between the threads of the screws and forced intoa pressure chamber I3 arranged at the opposite end of the casing Iwhence it is discharged through the outlet I 4.

In order to balance the axial thrust acting on the screw 8 caused by thedifference of pressure of the liquid in the chambers I3 and I2 the screw8 at one end has a piston I5 and at the other end a smaller piston I6.The piston I5 runs with asmall clearance in a bore in the slee-ve Il,which by the working pressure is held with the annular part I8 pressedagainst the cover 2. The central screw-rotor is provided with an axialpassage IS, through which the low pressure end of the screw-rotorcommunicates with the chamber I2 through branch passages 36, thus`connecting the chamber 20 enclosed between the sleeve Il and the cover2 with the chamber I2`. At the right hand end the draining passage I9 isclosed by means of a screw plug 31 inserted from the end of the pistonI6. The side screws 9 are also provided with axial passages 2| extendingthrough the shaft ends 24 to the end surfaces of the pistons 22 runningin cylindrical sleeves 23. Bores 25 in these sleeves 23 facecorresponding bores in the cover 3 and communicate with a passage 2 6 inthe cover 3. The piston I 8 runs in another cylindrical sleeve 21, theinside of which is connected with the passage 26 in the same Way.

By means of this arrangement not only are the side screws 9 balanced bytheir postons 22, but the central screw-rotor 8 is also balanced bymeans of its piston i6, the piston i6 "being subjected to the deliverypressure of the pump through bores 2l and 25 and passage 25.

When the pump is not working and there is no pressure in the pump, thescrews 8 and 9 are carried only by the relatively short part of thesleeve, this being the sole part which is rigidly` tted to the casing,all the other parts being carried by the screws.

When the pump is started the pressure in the chamber i3 will exceed thatin the chamber I2 as well as that in the space between the parts of thesleeve.

As a result the free part 6 of the sleeve is pressed against the fixedpart 5. In order to obtain a. safe grip between the parts 5 and 6 theirend surfaces facing each other are provided with annular extensions 2 8.Further the pressure of the liquid in the cham-ber i3 forces the sleeveVl against the inside cover 2S, which is supported by the cover 2 and atthe same time the cylindrical sl-eeves 23 and 2? are pressed against thecover 3. A spring Sii is placed between the sleeves and Il in order toensure co-ntact between the parts 5 and as well as between the sleeve I1and the inside cover 2S from the start of the pump.

In the embodiment according to Figs. 3 and l only two *screws are usedand the casing l itself is divided. The right part of the casing i inFig. 3 is integral with the sleeve, the bores for the screws beingexecuted in the casing itself. The left part encloses a separate sleeve6 fitted as previously shown in Fig. 1. An elastic O-ring 3l preventsentry of pressure between the sleeve E and the casing l. Another O-ring32 is placed in a groove in the end surface of the sleeve 6 just outsidethe bores for the screws 8, A bore 35 ending in the chamber I2 drainsthe space between the O-rings 3l and 32. The fluid pressure on thesleeve 6 is carried by the annular extension 28 along its circumference.To drain the space outside the sleeve a number of grooves 23 across theannular extension 28 are provided.

The invention may be varied within a wide scope and the tighteningdevices 3l, 32 with the draining passage 35 may if desired also beutilized in the embodiment illustrated in Figs. 1-2.

The balancing pistons of the screws shown in the figures are notessential for the present invention, but they are of some consequencefor the avoiding of any misalignrnent of the parts.

To those skilled in the art it is evident that the details of theinvention are not limited by the combinations described.

What is claimed as new and desired to be secured by Letters Patent is:

l. A rotary pump having a housing with an inlet and an outlet, aplurality of intermeshing, parallel, rotary screws, and a sleeve withintersecting, parallel bores, closely fitting the outside perimeter-s ofsaid screws, the sleeve being divided perpendicularly to the axes of thebores into parts freely movable in relation to each other, one of theparts of the sleeve being fixed in the housing, and the other part beingexposed at its outer end to said outlet and in clearance relationship tothe housing for freedom to properly align itsehC with the firstmentioned part when it is urged towards the first mentioned part by theWorking pressure of the pump.

`2. A. rotary pump having a housing with an inlet and an outlet, aplurality of intermeshing, parallel, rotary screws, and a sleeve withintersecting, parallel bores, closely tting the outside perimeters ofsaid screws, the sleeve being divided perpendicularly to the axes of thebores into parts freely movable in relation to each other, one of theparts of the sleeve being xed in the housing, and the other part beingexposed at its outer end to said outlet and in clearance relationship tothe housing for freedom to properly align itself with the firstmentioned part when it is -urged towards the first mentioned part by theworking pressure of the pump, the adjacent ends of said 'parts havingannular fitting surfaces.

3. A rotary pump having a housing with an inlet and an outlet, aplurality of int-ermeshing, parallel, rotary screws, and a sleeve withintersecting, parallel bores, closely fitting the outside perimeters ofsaid screws, the sleeve being divided perpendicularly to the axes of thebores into parts freely movable in relation to each other, one of theparts of the sleeve being fixed in the housing, and the other part'being exposed at its outer end to said outlet and in clearancerelationship to the housing for freedom to properly align itself withthe rst mentioned part when it is urged towards the iirst mentioned partby the workinfr pressure of the pump, theiirst mentioned 'part' beingintegral with the housing.

li. A rotary-pump having a, housing with an inlet and an outlet, apluralityrof intermeshing, parallel, yrotary screws', anda sleeve withintersecting, parallel bores; closely fitting the outside perimeter-s ofsaid screws, the sleeve being divided perpendicularly to the'axes of thebores into parts freely movable in relation to each other, one of theparts of the sleeve being fixed in the housing, and the other part beingexposed at its outer end to said outlet and in clearance relationship tothe housing for lfreedom to properly align itself with the firstmentioned part when it is urged towards the first mentioned part by theworking pressure of the pump, the adjacent ends of said parts havingannular fitting surfaces, the rst mentioned part being integral with thehousing.

5. A rotary pump having a housing with an inlet and an outlet, aplurality of intermeshing. parallel, rotary screws, and a sleeve withintersecting, parallel bores, closely fitting the outside perimeters ofsaid screws, the sleeve being divided perpendicularly to the axes of thebores into parts freely movable in relation to each other. one of theparts of the sleeve being fixed in the housing, and the other part beingexposed at its outer end to said outlet and in clearance relationship tothe housing for freedom to properly align itself with the firstmentioned part when it is urged towards the first mentioned part by theworking pressure of the pump, and a resilient ring surrounding thesecond mentioned part and engaging the housing.

CARL OSCAR TORSTEN MONTELIUS. l

REFERENCES CITED The following references are of record in the file ofthis patent:

FOREIGN PATENTS Great Britain Dec. 3, 1941

